The invention relates to a device, particularly for the digital measuring of force. Furthermore, with this device, measurement can be made also of the dimension of travel and of dimensions that can be derived from force and travel.
As per DDR Letters Patent No. 94,905, a device for the direct digital measuring of force is known, containing a measuring element which consists of several transparent plates firmly fastened to each other. Force, as measured dimension, acts onto one plate of the measuring element, the so-called diaphragm. The air gap formed by this diaphragm and the plate located opposite to it, is so shaped, that on deflection of the diaphragm and on transmission of parallel monochromatic light through the measuring element, an interferential splitting of the torsional fringes will occur. With the aid of photoelectric receivers, certain points at the interferential splitting of the torsional fringes will be scanned. Optimal conditions will result, when the interferential fringe will rotate from an inclined initial position at the origin of the measuring range, to a position, symmetrical to the initial position, at the end of the measuring range. By calibrating the receiver in the y direction, the storage volume of the available characters, appurtenant to the measuring range, is determined. By distance calibrating of the receivers in the x direction, the desired phase position of the output signals can be achieved.
In this device, the storage size of the available characters allotted to the measuring range is determined by the distance of the scanning point of the receiver to the x axis. This allotment will thus change when, for instance by fluctuations in temperature, the relative positions between measuring element, the optical image system and the photoelectrical receiver are being changed.
By reason of distribution of the torsional fringes, the distance of interference fringes will remain constant in the x direction, but will change however in the y direction, depending upon the value of the dimension measured. Thus, the number of interference fringes that can be evaluated, is limited by that distance of the interference fringes which can still be evaluated photoelectrically.
If the force acts upon the diaphragm from a point out-of-center, torsion of the diaphragm will occur, whereby a change occurs in the distance of the interference fringes in the x direction, and thus also in the phase difference between the output signals.
The firmly connected plates forming the measuring element must be made of a high-quality and transparent material.
Furthermore, the plates must have a high surface quality and dimensional stability, in order to achieve the desired geometry of the air gap.
It is not possible to produce the distortion body from one piece, since the surfaces enclosing the air gap must be polished.